蝗灾是由于蝗虫数量的季节消长引起的。( )

数据库的运行管理功能主要是指 【18】 。

Air is an odorless (无气味的), invisible (看不见的) gas that surrounds the earth. It is everywhere on the planet. An “empty” drinking glass and an “empty” room, to give two examples, are not really empty. Each is filled with air. When the glass is filled with water, the water pushes the air out of the glass.

Air, as a gas, has no definite (明确的) shape, but, because it is matter, it takes up space. It is easy to prove that air is something that takes up space. Stuff a dry handkerchief into the bottom（底部） of a glass so that it will not fall out when the glass is turned upside-down. Push the upside-down glass; hold it straight into a jar of water till the glass is completely covered. When the glass is taken out of water, the handkerchief will be dry. The air inside the glass takes up space and keeps the water from coming in.

小题1:What does the underlined word “Stuff” (in Paragraph 2) mean?

A．Press tightly.

B．Take out.

C．Put down.

D．Turn fully.小题2:The writer tells us that _______.

A．the experiment is done in the laboratory

B．the experiment is done outside the room

C．the experiment is easily done

D．the experiment is carried out indoors小题3:Which of the following pictures gives us the correct result?

( W—water;  A—air;  H—handkerchief )

镇吐作用强，无镇静作用，锥体系反应轻的药物是

A．氟哌利多
B．舒必利
C．氟哌噻吨
D．氯氮平
E．五氟利多

以下各项关于层流与紊流说法不正确的是（）。

A、所谓层流状态是指油液在流动时，像是一层层不同流速的油在流动，各层的质点平行于管子轴线方向而不杂乱

B、流速是判别层流与紊流的标准

C、所谓紊流状态，是指油液在流动时，质点除做轴向运动外，还有一些质点做横向涡流运动

D、液体在管道中流速较低时，液体做层流运动，当流速较高时，液体则做紊流运动